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Passive Transport/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby An animation shows a man, Tim, sitting on a chair next to a computer screen. He is typing on the keyboard. A robot, Moby, enters the screen from the left. The view switches to a close-up of Tim. An animation of an aroma traveling through the air is shown passing by Tim’s nose. Tim sniffs. TIM: Are you wearing my mom’s perfume? The animation shows Moby is holding a piece of paper. The aroma seems to be coming from the paper. MOBY: Beep. A close-up of Moby shows him raising his hand. In his hand, he is carrying a perfume bottle with a stopper. TIM: That’s . . . uh . . . uh . . . Tim sneezes. Moby holds up the stain-filled sheet of paper. Tim reads from the typed letter. TIM: Dear Tim and Moby, How do our cells take in oxygen and other stuff? from Mahmoud. Moby flicks the paper up and down a couple of times. Drops of liquid fly off the paper. TIM: Cells get everything they need from their environment. A drawing shows a cell in cross-section. It has a blue sphere in the center and several layers around the sphere. It appears to have an outermost membrane. Various objects are within the membrane layer. Text reads: cell. TIM: The cells in your body hang out in an environment of blood, which contains oxygen, water, food, and whatever else they might need to function. An animation of blood moving along a pathway within a body is shown. As Tim speaks the words “oxygen,” “water,” and “food,” icons for these items appear. The oxygen icon looks like two orange spheres stuck together. The water icon looks like an orange sphere with two small attached white spheres. The food icon consists of a large number of different-colored spheres clumped together. Text reads: blood. MOBY: Beep? TIM: How does stuff get in and out of cells? Well, cells are surrounded by protective membranes. The drawing shows the cell in cross-section again. A close-up shows the outer layer of the cell. The label “cell membrane” points to this layer. TIM: But the membranes are selectively permeable — they let some things in and keep others out. An animation shows the icons representing the water and oxygen, and other clumps of spheres, floating about, both inside and outside the membrane. The water and oxygen icons pass through the membrane while others bounce off it. An icon that is not water or oxygen bounces off as “keep others out” is spoken. Text reads: selectively permeable. TIM: The membranes have tiny pores in them pores that allow certain substances, like water and oxygen, to pass through. In the animation, openings are shown in the membrane. The label “pores” has lines drawn from it that point to the openings. TIM: These substances can move through the membrane without the use of energy on the cell’s part. This movement is called passive transport — the cell doesn’t have to do anything to make it happen. It just sits there and lets the water, nutrients, and whatever else pass through. A cartoon shows a cell lounging around. The cell is wearing a pair of dark sunglasses and has a mixed drink next to him. The glass holding the drink has a lemon wedge on the rim, and a straw and an umbrella sticking out. Spheres are passing in and out of the cell while he lounges. TIM: Now, passive transport works by diffusion. That’s the natural spreading of particles through a liquid or gas. An animation shows a drop of some liquid falling into a pool of liquid. As the drop hits the liquid, a small portion of the liquid turns a darker color. This darker color then spreads outward until the entire pool becomes dark. Text reads: diffusion. TIM: Molecules naturally spread from high concentration areas to low concentration areas. An animations shows a close-up of molecules. There are more molecules on the right side of the screen. A caption on the left reads: low concentration. A caption on the right reads: high concentration. As the molecules move around, more move over to the left side of the screen until the molecules appear to be spread out evenly. TIM: These differences in concentration are called gradients. The animation shows the close-up of the molecules with more molecules on the right. A large arrow labeled “concentration gradient” points from the right to the left. TIM: Substances are said to diffuse down concentration gradients. Eventually, everything gets evenly mixed, and a state of equilibrium, or balance, is reached. In the animation, the molecules move around until they appear to be equally distributed around the screen. A double-headed arrow labeled “equilibrium” appears. TIM: If you’ve ever smelled flowers from across a room, you’ve experienced the effects of diffusion. An image shows a room. There is a chair next to a table which is holding a vase of flowers. A red glow radiates outward from the flowers and fills the room. MOBY: Beep? TIM: How does diffusion relate to our cells? Okay, let’s say there are more oxygen molecules outside a cell than inside. A drawing appears showing a close-up of a cell membrane. There are a large number of molecules floating around outside the cell. Inside the cell there are only two molecules. An arrow reading “concentration gradient” points from the outside of the cell to the inside. TIM: Because oxygen can pass through a cell membrane, diffusion will even out the concentration of oxygen molecules inside and outside the cell. An animation shows molecules passing into the cell. Once there are about the same number of molecules outside the cell as inside, a double-headed arrow labeled “equilibrium” appears. TIM: That’s how our cells get the oxygen and water they need to survive. The animation shows both oxygen and water molecules, now equally distributed both inside and outside the cell. TIM: Diffusion actually works for getting rid of substances, too. As carbon dioxide builds up inside a cell, it diffuses through the membrane and into the surrounding blood, which has a lower C O 2 concentration. In the animation of the cell, all of the molecules are depicted as three spheres in a row, colored orange, black, orange. There are more of these molecules inside the cell. An arrow labeled “concentration gradient” points from the inside of the cell to the outside. The molecules move around, with many moving outside the cell. When the molecules seem about equally distributed, a double-headed arrow labeled “equilibrium” appears. TIM: Healthy cells maintain a state of dynamic equilibrium — substances are constantly diffusing across cell membranes to even out the differences. The animation shows molecules of all sorts moving both in and out of the cell. Text reads: dynamic equilibrium. MOBY: Beep? TIM: Sometimes a cell will move substances up the concentration gradient. An animation shows a cell with more molecules inside than outside. An arrow labeled “concentration gradient” points from inside the cell to the outside. Cells from the outside move into the cell. TIM: And food particles, like glucose, are too big to get through the gaps in the cell membrane. An animation appears showing a large molecule trying to get into a cell, but bouncing off the outer membrane. TIM: When a cell has to use energy to move substances across its membrane, it’s called active transport. But that’s really a whole other subject. The animation shows the large glucose molecule entering into the middle of the membrane through an opening facing outward. The particle then sits in a chamber inside the membrane. The outward-facing entrance hole closes and an inward-facing exit hole opens up. The glucose molecule then exits the chamber and enters the interior of the cell. A caption reads “active transport.” Energy spheres with a lightning bolt icon labeled Upper A Upper T Upper P are shown inside the cell. MOBY: Beep? TIM: Uh . . . no . . . no . . . I . . . I just won’t discuss it right now. Moby frowns at Tim who is sitting at the computer. MOBY: Beep! TIM: Well, whatever. Moby looks at Tim who is typing on the computer. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts